1. Field of the Invention
The present invention relates to a projection apparatus, an elevation angle control method therefor, and a recording medium.
2. Description of the Related Art
There exists a distance measuring apparatus or a distance measuring apparatus with an AF (Auto focus) sensor module for a projection apparatus (see, for example, Unexamined Japanese Patent Application KOKAI Publication No. 2005-6228).
On the other hand, projection apparatuses equipped with a zoom mechanism unit are increasingly becoming popular. Zooming is achieved by changing the focal distance of the projection apparatus, and the ratio of the focal distance when the zoom is set to the telescopic side to the focal distance when the zoom is set to the wide side, is called the zoom magnification.
Conventionally, in case a projection apparatus is configured in such-a way that a center of the display unit does not match with the optical axis of a projection lens, the center of the projection area of a projection apparatus will be shifted upward, as the zoom magnification is changed. That is, as best shown in FIG. 9, when the zoom magnification of the projector 51 (projection apparatus) is changed from telescopic to middle, and to wide mode, the projection area changes from Area_t(telescopic) to Area_m(middle), and to Area_w(wide), and accordingly the center of each projection area slightly shifts upward in the elevated (upward) direction.
Because the distance measuring apparatus is fixed at a given elevation angle, the direction to its distance measuring center does not change. With zoom being set to the telescopic mode, the center position of the projection area substantially matches with a position indicated by the direction to the distance measuring center. With zoom being set to the middle or the wide mode, however, the position indicated by the direction to the distance measuring center is shifted downward relative to the center of the projection area of Area_m or Area_w.
Auto focus control requires information on the distance to the center of the projection area. With the zoom set to the telescopic side, the distance to the center that is measured by the distance measuring apparatus substantially matches with the distance to the center position of the projection area. However, when the zoom is changed to the middle or to the wide side, the distance measuring apparatus will measure the distance to the position shifted from the center of the projection area rather than the distance to the center of the projection area. Accordingly, the distance to the center position of the projection area cannot be measured accurately, resulting in lower performance of auto focus control.
In view of the conventional problem, it is an object of the present invention to provide a projection apparatus, an elevation angle control method therefor and a recording medium, which can accurately measure a distance.